Photographic emulsions of silver salts in hydrophilic polymers of 1, 3-dioxolane



Patented Feb. 17, 1948 PHOTOGRAPHIC EMULSIONS' OF" SILVER SALTS IN HYDROPHILIC- POLYMERS F 1,3-DIOXOLAN E Theodore Le Sueur Cairns, Roselle, andDavid Malcolm McQueen, Newark; Del.,assignors to E. I. du Pont de Nemour's'z Compantg wilmington, Del., a corporation of Delaware- No Drawing. Application November 27, 1944,

Serial No. 565,402

4 Claims. (Cl. 95-7) This invention relates to photographic emulsions and emulsion layers composed of hydrophilic polymers of 1,3-dioxolane and to photographic elements containing the same.

In the past many difierent materials have been used in photographic emulsions as bi'ndingagents for the light-sensitive components. The most widely used binder, gelatin, is well adapted to this use because it servesas a goodprotective colloid for silver halides in fiuid emulsions and when coated on a suitable support and dried, these emulsions form films which are permeable to the aqueous solutions used to develop the photographic'images. However, gelatin has some disadvantagesamongwhich ma be mentionedits high cost, which is due lar'gely'to the timeconsuming' preparatory processes necessary to give a product of high-purity, Further, gelatin is not uniform in quality and varies from one lot to another. Otherdisadvantages of gelatin include its susceptibiilty to bacterial attack and the deleterious efiect of changing humidity.

That is, at high relative humidity gelatin films become soft and weak unless given a special hardening treatment and under conditions of low relative humidity they are very brittle.

Other materials have been tried as binding agents but have met with little success. For example, collodion, one of the first binders used for silver halides, is 'very insensitive to water and mustbe processed inspecial fashion. Albumin, agar-agar, casein, and other natural colloids have also been tried as emulsion binders but all have many'disadvantages such as high cost, low film strength, too high or too'low water sensitivity, etc. More recently, it has been proposed to use certain derivatives of polyvinyl alcohol and cellulose derivatives. best binder now available and it is used in almost all light-sensitive emulsions that are commercially available.

An object of this invention is to provide new photographic emulsions and emulsion layers which are free from the disadvantages of gelatin; Another'object is to provide such emulsions which can be prepared in a simple and economical manner. Another object is to provide new photographic emulsions from synthetic materials which are of uniform quality. A still further object is to provide novel photographic emulsions which are not susceptible to bacterial attack. Still other objects'are' to reduce the cost ofphotographic emulsionsan'cl' improve their resistance" to changes-of humidity.

It" hasbeen foundthat useful photographic However, gelatin remains the compositions can be made by incorporating "radiation-sensitive materials in a hydroph'ilic polymer of 1,3-dioxolane.- This maybe accomplished by colloidally dissolving'the'polymer of 1,3-dioX- olane in water and admixing the light sensitive material therewith After the light-sensitive material has been uniformly dispersed, the resulting solution may be further modified and coated onto a support to form a light-sensitive layer.

In a preferred mode of the invention, the hydrophilic polymer of 1,3-dioxolane is dissolved in an aqueous solution and light-sensitive silver halides are precipitated therein. This 'mayadvantageously be accomplished by dissolving a 501- uble ionizable halide, e. g., sodium, potassium or ammonium chloride or bromide, etc., in the solution of the polymer of 1,3'-dioxolane and adding an aqueoussolution of a soluble ionizable silver salt, e. g., silver nitrate, with stirring. The re-' sulting emulsion can then be ripened, chilled'or precipitated, digested and modified by the addition of more of the same 1,3-dioxolane polymer, general emulsion sensitizers, anti-fogging agents, spectral sensitizing dyes, preservatives, hardeners and/or color .form'e'rs, etc., and coated onto a temporary or permanent support or onto a layer of such support. Unwashed emulsions can be used but in general'it is desirable to remove" the excess soluble salts. For example, theunwashed emulsion may be precipitated with a salt-solution such as an aqueous sodium sulfate solution, washed'free from soluble'salts and then red-issolved in afresh 1,3-dioxolane polymertsolution.

After the light-sensitive 1,3-dioxola-ne polymer solution is prepared for coating it may be depos ited, in the'sam'e way that gelatin silver-halide solutions are coated, upon a suitable support, e. g., metal, paper,-glass, or a transparent film such as cellulose nitrate; cellulose acetate, nylon, etc, anddried. The resulting element can then be exposed and processed to positive or negative pictures in the same manner as ordinary gelatino silver halide photographic'elements.

The hydrophilicpolymers of 1,3-dioxolan'e which have been found to be useful in the photographic emulsions and layers described above can be made after the manner described in. Gresham applicationserial No. 392,124, filed May- If desired, the temperature of the reaction, especially when polymerization is carried out at the boiling point of the cyclic compound, may be controlled by varying the pressure on the boiling reactants.

It has been found advantageous to efiect the polymerization in the presence of a catalyst such, for example, as sulfuric acid, phosphoric acid, bydrochloric acid, hydrofluoric acid (alone or with BF's) boron fluoride (including its complexes with water, acids, esters, alcohols, and the like), paratoluenesulfonic acid, camphor sulfonic acid and other acid catalysts of this general nature. Friedel-Crafts type catalysts other than BF; may be used such as AlCls, AlBrs, FeCla, etc.. as may be inorganic acids generally, and their acid salts such as sodium acid sulfate, sodium acid phosphate. etc.

The reaction is carried out for an extended period until solid polymers which are capable of cold drawing are formed. This reaction is preferably carried out at moderate temperatures, e. g., 20 to 80 C. at about normal pressure, for a period of several days using boron trifiuoride as a catalyst.

It is believed that the polymerization proceeds in accordance with the equation o-cn,

wherein a: is at least 135. The polymers comprehended by the present invention in terms of molecular weight have a weight of at least 10,000. The useful polymers can best be selected by their viscosity characteristics. They should have a relative viscosity of at least 1.04 (determined as 0.1% in chloroform) and from 1.06 to 1.20 represents a practical range. By relative viscosity is meant the viscosity in comparison to that of pure chloroform to which is assigned a value of 1.00.

All viscosities are at 25 C.

The 1.3-dioxolane polymers used in accordance with this invention are generally soluble in water at to 60 C. to the extent of 5-20% or more but, if desired, water containing small amounts (IO-20%) of a water-soluble organic solvent, e. g., ethanol, methanol or another monohydric alcohol of less than 4 carbon atoms, may be employed. Aqueous solutions of the hydrophilic polymers of 1,3-dioxolane are stable at ordinary temperatures but when heated to 80 C. to 100 C. precipitation of the polymers occurs. This unusual property may be used advantageously in manufacturing the polymers for this invention.

The invention will be further illustrated by the following examples. All parts are by weight.

Example I .A reaction mixture containing 400 parts of 1,3- dioxclane and about 0.2 part of boron trifluoride is allowed to stand at room temperature for 5 days. At the end of this time, the polymer, which is a hard, tough, resin-like solid, is converted to thin shavings which are dissolved in 0.1% aqueous NHiOl-l at to 60 C. and precipitated from this solution at 100 C. after adding 3-4 parts of NaOH for every 50 parts of polymer dissolved; The catalyst-free polymer is then spread on a smooth surface such as a glass or metal plate and allowed to dry for 5 to 50 hours. If desired, the drying process may be accelerated by placing the polymer in a vacuum oven and drying at 50 C. The dry polymer is cut into small pieces and pressed into a thin film by heating on the platens of a press at C. under a pressure of approximately 100 lbs/sq. in. for 5-30 minutes. The properties of this treated film are:

Appearance Tough, elastic, white. Tensile strength 3020 lbs/sq. in, Elongation at break 425%.

Elongation recovery 325%.

Film appearance"--. Colorless, cloudy, flexible.

- Cold draws well and stretches in the cold drawn state.

Molecular weight 86,000 (determined by viscosity of a chloroform solution).

Melting point 63-70 C.

Example II A mixture is made of 15 parts of 3 N ammonium bromide, 2 parts of 0.5 N potassium iodide and 5.0 parts of a 10% solution of the hydrophilic polymer of 1,3-dioxolane (prepared according to Example I) and, while stirring at 40 C., a solution of 10 parts of 3 N solution of silver nitrate containing sufficient ammonium hydroxide to give a clear solution is added slowly. The photographic emulsion thus formed is stirred at 40 C. for 15-60 minutes, cooled, and coated on a support. After drying, the photographic element is exposed to an object and developed by immersion at 18-30 C. in a standard p-methylaminophenolhydroquinone developer such as the following:

5 Parts p-Methylaminophenol sulfate 3 Sodium sulfite (anhydrous) 45 Hydroquinone 12 Sodium carbonate (anhydrous) 67.5 Potassium bromide 1.9

Water to make 1000 The developed picture is fixed by bathing in a 25% solution of sodium thiosulfate (hypo), freed of soluble salts by washing, and dried. The resulting black and white picture has density gradations complementary to the object scene to which the element was exposed.

Example III A photographic silver halide emulsion prepared as in Example 11 is precipitated by adding an excess of saturated solution of sodium sulfate and then washed free of soluble salts in running water. The emulsion is then redissolved in 50 parts of 10% polymer solution and digested at 50-60 C. for 30-60 minutes; The washed emulsion thus obtained is coated and processed as in Example H to obtain a black and white negative picture.

Example IV Example V A reaction mixture containing 400 parts of 1,3- dioxolane and about 0.2 part of boron trifiuoride was allowed to stand for 13 days at 6 C. In three days the mixture became viscous and in 7 days hadirsolidified. Thin; shavings: of: the resultant solid polymer were dissolved in approximately 0.1% aqueous NH4OH'. at- 50:-60 C. and precipitated from thissolution-at 100 C. afteradding 3+4rparts of" sodium hydroxide-for every 50' g. ofapolymer: dissolved. The catalyst-free polymer iswthen spread. ona smooth surface" such as a glass or metal plate..and :allowed.todryfor"5 to 50 hours. If desired, thedrying process may be accelerated by placing the polymer in a vacuum oven anddrying at 50 C. The dry polymer'is cut-into small pieces and pressed into athin film by heating on theplatens of apress at 100 C. under a: pressure of approximately 100 lbs. /sq.- in.

for 5-3-0 minutes The properties of this treated film are:

Appearance Tough, elastic, white. Tensile strength 4520 lbs./sq. in..

Molecular weight 196,000 (determined by viscosity method in chloroform) Cold drawn film:

Tensilestrength 5530 lbs/sq. in.

Elongation at break 200% Elongation recovery .to 50 Example "VI A'mixture is made of 15 parts of 3 N ammonium bromide, 2 parts of 0.5 N potassium iodide and 5.0 parts of a solution of the hydrophilic polymer of 1,3-dioxolane (prepared according to Example V) and, while stirring at 40 C., a solution of 10 parts of 3 'N'solution of silver nitrate containing suificient ammonium hydroxide to give a clear solution is added slowly. The photographic emulsion thus formed is stirredat 40 C. for -60 minutes, cooled, and coated on a support. After drying, the photographic element is exposed to an object and developed by immersion at 18-30 C. in a standard p-methylaminophenol-hydroquinone developer such as the following:

Parts p-Methylaminophenol sulfate 3 Sodium sulfite (anhydrous) 45 Hydroquinone 12 Sodium carbonate (anhydrous) 67.5 Potassium bromide 1.9 Water to make 1000 The developed picture is fixed by bathing in a solution of sodium thiosulfate (hypo), freed of soluble salts by washing, and dried. The resulting black and white picture has density gradations complementary to the object scene to which the element Was exposed. In preparing polymers of 1,3-dioxolane, monofunctional compounds can be added to the polymerization reaction mixture in small amounts in order to react with the polymer units at the end of the polymeric chain provided, however, that the amount of monofunctional compound added does not reduce the molecular weight of the polymer below 10,000. Such monofunctional compounds include carboxylic acids and their acid chlorides and anhydrides, sulfonic acids, sulfonyl halides, and the valeryl-v 1 0111013616,. bienzoyl chloride; and? toluoyl chloride and the corresponding-acids: and anhye drides, ethane sulfonylrchloride, cyclohexanesulfonyl I chloride; benzene? sulfonyl chloride, para-.- toluenesultonic. acid,';,' etc. When used: small amountsas chain terminating: agents, these. compounds do not .modify tov anymaterial extent'rthe properties of the?.poly-1,3.-dioxolane: as ar gelatin substitute:

The. inventiongamoreover; is-not:.1imited: to. the specific .light-sensitive material described-1m .the above-detailed. examples. On thecontrary, var.- ious.:other simple-and mixed silver-halides: may be usediastthe lightsensitivematerials in like manner. Mixtures: of. silver bromides; chlorides and/oriiodides can be made. by. adding mixtures of soluble salts :of these. halides in like manner.- Other useful-soluble. halides includepotassium bromide, potassium iodide, sodium and potassium chlorides andiodidemetc. Other useful soluble silver salts include silver sulfamate,silversulfate; silver citrate and silver acetate.-

Still other radiation-sensitiveor light-sensitive materials such as light sensitive diazonium compounds, ammonium-.bichromate, fulgides, etc. can beusediin the emulsionsand emulsion layers com posedofthe above-hydrophil-ic1,3-dioxo1ane poly mers.

The emulsions, after formation, are-preferably digested at a temperaturefrom40 to C. for a period of from 30 minutes to 6hours. During the digestion stage orzprior thereto, varioustypes of sensitizing agents, e.- g.,. sulfursensitizers such as. allylthioureas,.. thiocyanates, sodium :thiosulfate, allylthi'ocyanates, can be added; In addi-v tion, various. types of. optical. sensitizing dyes which modifythe: spectral characteristics 'ofithe resulting emulsions can beadded; Suitable sene sitizing dyes are described U. 8.: Patents 2,010,388, 2,079,376, 2,202,990, 2,202,991, 2,202,992, 2,278,461, 2,265,908, etc.

Various types of color formers or dye intermediates capable of forming quinoneimine or ammethine dyes on color-forming development can be incorporated in the emulsions. Thus, the phenols, naphthols, pyrazolones, acylacetamides, hydrindene, N-homophthalylamines, etc., particularly those of high molecular weight and which are immobile in gelatin emulsion layers can be used. Suitable color formers are described in U. S. Patents 2,108,602, 2,166,181, 2,178,612, 2,179,228, 2,179,238, 2,179,239, 2,182,815, 2,184,303, 2,186,849, 2,200,924, 2,283,276, and 2,328,652.

The hydrophilic 1,3-dioxolane polymer emulsions are normally used without other film-forming colloids. However, they are compatible to a limited extent with gelatin and certain other materials, such as cellulose derivatives, and these may be added to the light-sensitive compositions if desired.

The photographic elements of the present invention have a number of outstanding advantages over the prior art materials. For example, they are based on a material derived from formaldehyde and ethylene glycol and thus ofier substantial economic advantages. The photographic emulsions have great stability toward bacterial and fungal decomposition and this is also true of the coated photographic elements. This inertness is perhaps related to the chemical structure of the 1,3-dioxolane polymer which derives its hydrophilic character from the plurality of in 7 tralinear ether groups in contrast to other materials proposedas photographic colloids.

Surprisingly, Lthe hydrophilio .1 1,3-dioxolane polymers are alsosoluble in certain hydrocarbon solvents and, for. example, can be removedfrom the support by treatment; with benzene. .This is an advantage. in simplifying scrap film recovery. The filmelements also are freefrom the brittleness characteristics of gelatin films.

The light-sensitive film elements of the. present invention may be used, for example, as a tak-. ing stock (negative) as print stock.(positive) ,.or as reversal film, in the preparation. of films for microcopy, V-mail, inX-ray films, in,lithographic films and. in portrait materials. In addition, when diazonium salts .or ammonium bichromate are incorporatedin hydrophilic polymers of 1,31 dioxolane to form the light-sensitive layers, the film elements may be used in the graphic arts and in the reproduction, of lineHdrawings. vInfact, the film elementsof thisinvention can be used in any. way inwhich elements based on gelatin or collodion have been used.,

What is claimed is: V

1. A photographic.elementcomprising a supportbearing at least one layer composed of a hydrophilic, polymerof 1,3,dioxolane which polymer contains a large number or recurringunitsof the formula CH2OCHzCH2-,-O-, has a molecular weight of at least 10,000 and a relative viscosity/of 1.06 to 1.20,when ,present in an amount of 0.1% by weight in chloroform, said layer containing a light-sensitivesilver salt.

.2. A photographic element comprising. a.supportbearing at least'one layer composed of ahydrophilic polymerof 1,3- dioxolane which polymer contains a large number of recurring units of the formula CH2OCH2CH2O-, has a molecular weight of at least 10,000 and a relative viscosity of 1.06 to 1.20 when present in an amount of 0.1% by weight in chloroform said layer having unii'ormly dispersed therethrough light-sensitive silverhalides;

3. A photographic element comprising a sup"- port bearing. at least one'layer composed of a hydropholic polymer of 1,3-dioxolane said layer containing a color former and light-sensitive silver salts, said polymer having a largenumber of recurring units of the formula a molecular weight of at least 10, 00 and a rela-.- tive viscosity of 1.06 to 1.20 in chloroform when present in a concentration of 0. by weight.

4. A photographic emulsion composed of a hydrophilic polymer of 1,3-dioxolane whlchpoly-i mer contains a large number of recurring units of the formula CH2OCH2CHzO-, has a molecular weight of at least 10,000 and a relative viscosity of 1.06 to 1.20 when present in an amount of 0.1% by weight in chloroform said layer having dispersed therethrough a lightsensitive silver halide. THEODORE LE SUEUR CAIRNS.

DAVID MALCOLM MCQUEEN.

REFERENCES CITED The following references are of record in the file of this patent:-

UNITED STATES PATENTS Number Name L Date 5 2,187,081 Hodgins et al Jan. 16, 1940 2,276,322 Lowe Mar. 1'7, 1942 2,350,350 Gresham June 6,1944 2,360,477 Dahle 1 Oct. 1'1, 1944 2,366,737 Loder et a1. Jan. 9, 1945 f 2,394,910 Gresham May 6, 1941 FOREIGN PATENTS Number Country Date 496,049 Great Britain Nov. 21, 1938 

